Shim-Dex 14F Spark Plug Indexing Washer, 14mm Flat Seat, 24 Pk

These stackable spark plug shims from Shim-Dex rotate the ground of the spark plug at 30 degree intervals anywhere within 360 degrees so that you get the most out of your spark plugs without causing overheat and pre-ignition due to thread exposure.

• Shims rotate the spark plug ground at 30 degree intervals anywhere within 360 degrees
• You won't have to buy extra spark plugs to have them perfectly indexed
• Shims are reusable many times over
• Minimal or no thread exposure in the cylinder head that can overheat and cause pre-ignition
• Shims are so thin they will not adjust the gap too far out of the combustion chamber and negatively affect performance

Set includes (12) silver 60-degree shims, (12) black 90-degree shims and an indexing dial chart. 

Indexing Your Spark Plugs (PDF)